Seismic Swarm SVS20190829.1: Analysis of Activity Southeast of West Yellowstone, Montana

A seismic swarm designated SVS20190829.1 occurred 57 km southeast of West Yellowstone, Montana, from 21:20 on 29 August 2019 to 12:15 on 30 August 2019. Over 14 hours and 55 minutes, the event registered 43 earthquakes, with magnitudes ranging from 0.0 to 2.7 and focal depths primarily between 1 and 4 km.

The sequence began with low-magnitude events clustered tightly in time during the initial hours. Notable activity included a 2.6-magnitude quake at 21:33:01 on 29 August at 1 km depth and a 2.7-magnitude event at 22:24:12 at 2 km depth. Subsequent tremors tapered off, with the final recorded event at 12:15:57 on 30 August measuring 0.5 magnitude at 4 km depth. Depths remained shallow throughout, consistent with activity in the upper crust of the region.

This swarm fits within a broader pattern of seismicity in the area. Since 2000, 22 swarms have been documented near this location. Historical occurrences include five events in 2002, three each in 2009 and 2013, two in 2006, 2008, and 2018, and single instances in 2004, 2010, 2011, 2015, and 2016. Such clusters are characteristic of the Yellowstone volcanic system, where fluid migration and hydrothermal processes often trigger episodic earthquake sequences without producing a dominant mainshock.

Geologically, the swarm location lies on the Yellowstone Plateau, part of the active Snake River Plain-Yellowstone volcanic province. The region overlies a continental hotspot that has produced extensive basaltic and rhyolitic volcanism over millions of years. The most recent caldera-forming eruption occurred approximately 631,000 years ago, creating the Yellowstone Caldera. Ongoing deformation, heat flow, and seismicity reflect the presence of partial melt and hydrothermal fluids at shallow depths. Earthquake swarms here commonly arise from pore-pressure changes rather than tectonic fault rupture alone.

In context, swarm SVS20190829.1 exemplifies the background seismic unrest typical of the area. Magnitudes remained below 3.0, posing no significant hazard. Monitoring by regional networks continues to track such activity to better understand magmatic and hydrothermal dynamics beneath the plateau.

References

• SeismoSight internal swarm classification records
• USGS Earthquake Catalog (historical swarm statistics since 2000)